1. Field of the Invention
The present invention relates to a method and a device for encoding and decoding video signals.
2. Description of the Related Art
A number of standards have been suggested for compressing video signals. One well-known standard is MPEG, which has been adopted as a standard for recording movie content, etc., on a recording medium such as a DVD and is now in widespread use. Another well-known standard is H.264, which is expected to be used as a standard for high-quality TV broadcast signals in the future.
While TV broadcast signals require high bandwidth, it is difficult to allocate such high bandwidth for the type of wireless transmissions/receptions performed by mobile phones and notebook computers, for example. Thus, video compression standards for such devices must have high video signal compression efficiencies.
Such mobile devices have a variety of processing and so that a variety of forms corresponding to a variety of combinations of variables such as the number of frames transmitted per second, resolution, the number of bits per pixel, etc. This imposes a great burden on content providers.
In view of the above, content providers prepare high-bitrate compressed video signals for each video source and perform, when receiving a request from a mobile device, a process of decoding the compressed video signals and encoding it back into video signals suited to the video processing capabilities of a mobile device before providing the requested video signals to the mobile device. However, this method entails a transcoding procedure including decoding, scaling and encoding processes, and causes some time delay in providing the requested signals to the mobile device. The transcoding procedure also requires complex hardware and algorithms to cope with the wide variety of target encoding formats.
A Scalable Video Codec (SVC) has been developed in an attempt to overcome these problems. In this scheme, video signals are encoded into a sequence of pictures with the highest image quality while ensuring that a part of the encoded picture sequence (specifically, a partial sequence of pictures intermittently selected from the total sequence of pictures) can be used to represent the video signals with a low image quality.
Motion Compensated Temporal Filtering (MCTF) is an encoding and decoding scheme that has been suggested for use in the scalable video codec. However, the MCTF scheme requires a high compression efficiency (i.e., a high coding rate) for reducing the number of bits transmitted per second since it is highly likely to be applied to mobile communication where bandwidth is limited, as described above.
Although it is possible to represent low image-quality video signals by receiving and processing part of the sequence of pictures encoded in the scalable MCTF coding scheme as described above, there is still a problem in that the image quality is significantly reduced when the bitrate is lowered.